5.3.1 Chooses and manages the fitting of toric contact lenses

SELECTING A TORIC LENS

• Rx: 0.25DC

• Rx: 0.50DC / 0.75DC

• Rx: ≥0.75DC

Rx: 0.25DC

• Does not require toric lens

Rx: 0.50DC / 0.75DC

• Should be presented over the distance sphere rx to see if patient prefers vision

• If preferred, order toric lens with -0.75DC

Rx: ≥0.75DC

• If preferred, order toric lens with appropriate cyl

• Be aware of cyl over -2.50 as these patients may have limited choice in lenses

What should you consider when prescribing toric lenses for oblique astigmatism?

Patients will be more intolerable to uncorrected cyl when has an oblique axis

What questions should you add to the history for general symptoms?

Add extra questions regarding vision stability?

Does it worsen or get better on blink?

What should you assess when evaluating lens centration and coverage?

• Same checks as normal

• Monitor position of toric markings

• Check if the markings move significantly upon blinking

Settling time is ~5 minutes, this is the time the lens has been in the pt’s eye till they feel comfortable

What should you consider when assessing over-refraction?

Soft toric lens

• Normal over-refraction as normal.

• No using cross-cyl, just use lenses

• Check vision with ±0.25 DC difference in same axis

• No need to refine axis away from lens fit / sight test rx

What does CAAS stand for when assessing toric lens markings?

• C - Clockwise rotation

• A - Addition

• A - Anti-clockwise rotation

• S - Subtract

What should you consider when refitting an axis-corrected toric lens?

When refitting an axis corrected toric lens, you need the marking to be decentered similar to the original lens fit.

What are the three types of toric lens stabilisation designs?

• Prism ballast:

  • Lens is thicker at the bottom

  • Gravity, eyelid pressure, blink action help keep the lens in place

  • Cons: reduced oxygen transmission at the bottom of the corner; potential for discomfort

• Periballast:

  • Prism thickness confined to the peripheral lens area, away from the optic zone;

  • Improved oxygen transmission.

• Dynamic stabilisation:

  • Thinner lens at the top and bottom;

  • Upper and lower eyelids exert pressure on thin zones during blinking, keeping lenses stable.

  • Best oxygen transmission

  • Less suitable for patients with larger palpebral apertures.